1. Field of the Invention
The present invention relates to methods for determining the insertion depth of flow sensing probes, for measuring diameters of the pipes in which they are inserted and for detecting the fill depth of those pipes.
2. Background Information
Insertion probes for sensing flow rate are typically installed in a pipe using an insertion fitting mounted on the pipe. Compared to the more conventional full bore in-line flow sensors, which sense most, or all, of the fluid flowing through the pipe, these probes typically cost much less to purchase and install, and can be removed and reinstalled with relative case. Their main detriment is a reduction in measurement accuracy which occurs because probes generally sense the flow rate of only a small fraction of the total fluid in the pipe. There is also a potential for additional loss of accuracy if a probe is installed at other than a selected position, if the inside diameter of the pipe is not known accurately, or if the pipe is only partially filled. This invention relates to flow probe improvements for minimizing such accuracy degrading effects.
The flow rate through a round pipe is not the same everywhere through its flow cross section. Moreover, the distribution of local flow rates at the point of measurement also varies with the total volumetric flow rate. However, it is known that sensing the flow rate with a probe set at some selected points (e.g., approximately 11% of the pipe diameter in from the inside surface of the pipe) provides a good estimate of the total volumetric flow rate through the pipe. Deviation from that position is likely to produce additional and unnecessary measurement errors. Hence, arrangements for setting and checking the probe""s depth are important. Commercially available means for measuring the depths of some probes consist of linearly graduated portions of the probe""s stem or of attached parts that are observed visually. While these arrangements are satisfactory in some applications they are useless in others because of such factors such as poor lighting and cramped quarters during installation. Moreover, because of additional space required for the graduated portion, these probes can not be used in all installations. Because they usually determine penetration depth with respect to a known position of an insertion pipe fitting, these arrangements lead to errors if additional fittings are added during installation and change the distance between the reference point and the center of the pipe. Furthermore, the penetration depth cannot be readily determined remotely for checking the installation, as is often desired when troubleshooting. Hence, a significant problem in the flow probe art is that of accurately positioning a flow-sensing portion of the probe at a predetermined location within a pipe. Although selection of the predetermined location is an important part of flow measurement, it is not part of the present invention.
Insertion flow probes are often mounted on pipes which have been insufficiently or erroneously documented. Unfortunately, this usually occurs with pipes which are partially hidden or thermally insulated. Specifications and/or installation drawings are also often in error as to the internal diameter of the pipes. To counteract this source of flow sensing error a convenient means is required for measuring the internal diameter of the pipe.
It is therefore an object of the present invention to provide means that are essentially integral to the basic flow sensing probe and which enable its penetration depth and the internal diameter of the pipe that it is mounted on to be determined and observed both locally and remotely as desired.
The above and other objects are satisfied with a variety of sensing arrangement, which include both acoustic and optical means that are exemplified in accordance with various preferred embodiments of the present invention.
In one aspect of the invention a flow sensor comprising a flow probe having an insertable end for insertion into a pipe is improved by adding to it a position sensing device adjacent the insertable end of the probe. When in use, a flow sensing device can supply an electrical flow signal responsive to a rate at which a fluid in the pipe flows past a portion of the probe adjacent its insertable end, and the position sensing device can supply an electrical position signal responsive to a distance between the position sensing device and a selected portion of either a portion of the pipe or a portion of a probe insertion fitting into which the composite probe is inserted.
A feature of the invention is that it provides a method of positioning a flow probe within a pipe in which a fluid is flowing when an insertable end of the probe is inserted into the fluid through an insertion fitting. The probe, in this case, selectively provides either an electrical flow signal output representative of a rate of flow past a selected portion of the probe adjacent its insertable end or an electrical position signal responsive to a distance between a position sensing device adjacent the insertable end of the probe and either a selected portion of the pipe or a selected portion of the insertion fitting. The method comprises the steps of: a) inserting the insertable end of the probe into the pipe; b) energizing the position sensing device; c) displaying, to an operator, an indication of the measured distance; and d) moving the probe until the indication of distance reaches a selected valued.
Some embodiments of the invention use a transducer array capable of forming a steered beam of acoustic energy for both fluid flow sensing and pulse-echo distance measurement. In apparatus of this sort at least two transducers are mounted adjacent the insertable end of a probe. A first of these transducers comprises at least one transducer element and is selectively operable to generate a first acoustic beam directed at an acoustic transducer array and receive at least a portion of a second acoustic beam generated by the acoustic transducer array and to provide a first time-of-flight flow output responsive to the received beam. The second of these transducers comprises the transducer array, which is selectively operable to: a) generate the second acoustic beam directed at the first acoustic transducer; b) receive at least a portion of the first acoustic beam generated by the first transducer and provide a second time-of-flight flow output therefrom; c) generate a third acoustic beam that is not directed at the first acoustic transducer, but that is rather directed at a portion of the pipe in which the probe is installed; and d) receive a portion of the third acoustic beam and provide the pulse-echo output therefrom. Preferred embodiments of this sort provide a reflecting surface portion of the probe situated so that an acoustic beam generated by one or the other of the two transducers is reflected to the other transducer.
A first specific embodiment of the invention comprises a flow sensing turbine probe adjacent its insertable end. A probe of this sort is taught in Feller""s U.S. Pat. No. 4,829,833, the disclosure of which is herein incorporated by reference. The probe also holds a pulse-echo distance transducer which is periodically activated to produce bursts of acoustic energy directed at an inside surface of the pipe distal from the probe insertion fitting used to mount the sensor. The acoustic echoes are received by the transducer and amplified to produce corresponding electrical pulses. The measurement of the difference in time between the transmitted and received pulses is proportional to the distance separating the transducer and the inside pipe surface across from the transducer. That distance is added to the distance from the transducer to the center of the flow sensing element on the flow probe, the total then being subtracted from the known inside diameter of the pipe to yield the insertion depth. This addition and subtraction of distances is ideally performed electronically and results in a local or remote display of the net insertion depth. Acoustic sounding techniques for measuring distance as may be found in current art sonar and other acoustic instrumentation are employed.
A second specific embodiment is similar to the first embodiment with the main exception being that the transducer points in the opposite direction (e.g., upwards in the depiction of FIG. 2) to direct its bursts of acoustic energy toward and receive their echoes from the upper inside surface of the pipe. The insertion depth is then determined by adding the acoustically measured distance to the distance between the transducer and center of the flow sensing means of the flow probe. By incorporating two transducers on a single probe, one facing up and the other down, each transducer can measure the distance to the pipe surface that it faces. These distances can be combined along with the known distance between the transducers to yield the pipe diameter. In such an arrangement, it is economical to use a single set of distance measuring electronics which is switched between the two transducers and provides the distance summation.
In a third specific embodiment, an acoustic transducer is located so as to project its acoustic energy and receive the echoes in a direction generally along an axis of the pipe. As the probe is inserted into the pipe through a probe insertion fitting this results in the reception of very strong, short transit time echoes that are abruptly followed by very weak, long transit time echoes when the transducer moves from the insertion fitting into the pipe and the pulse-echo acoustic energy travels across the length of the pipe rather than being promptly reflected back by the pipe at its opening or by the associated fittings. The insertion location corresponding to that change in the echo characteristics is then a reference point from which the insertion depth may be determined. Electronics incorporating distance measuring principles may be incorporated here. However, the electronics may also be simplified to detect only the change in echo magnitude as a linear measurement is no longer needed once the reference point has been determined.
A fourth specific embodiment is similar in principle to the third preferred embodiment, but photoelectric rather than acoustic energy is used for the distance sensing. Here, a photoelectric emitter and detector are employed either directly at the flow sensing location or remotely through fiber optics to detect the change in reflection intensity of the emitted photo energy as the probe is inserted and the emitter-detector pair pass from the probe insertion fitting into the pipe.
A fifth specific embodiment utilizes one of the already existing transducers in an acoustic transit time flow sensing probe that operates as described in the Feller""s U.S. Pat. No. 6,178,827, the disclosure of which is herein incorporated by reference. In this embodiment the selected transducer is temporarily disconnected from the flow rate measurement electronics when a distance measurement is desired and connected instead to the distance measuring electronics as in the first embodiment. The probe""s acoustic reflector 20, of FIG. 1, is made as narrow as possible consistent with good flow rate measurement, in order to pose the least interference with the acoustic waves being directed to and received from the pipe wall. The reflector may also be offset from center to further clear the path between the transducer and wall, although the reflector is angled slightly for maximum acoustic reflection of the acoustic energy between the transducers as required when measuring flow rate. The transducer angles may also be selected in order to achieve the best compromise in acoustic energy propagation efficiency between the two modes of operation. The operating frequency for distance measurement may also be changed to widen or distort its acoustic projection and to reduce fluid attenuation losses so that a larger portion of that energy returns as an echo from the pipe to the transducer. An echo will be present from the acoustic energy reflecting off the other transducer which may be suppressed by nullifying the magnitude of that signal as a preset since its magnitude and time of occurrence is highly consistent.
The present invention is compatible with different types of flow sensing probes because it can operate independent of the flow sensing method employed and requires little space for its implementation. Some examples of the types of flow probes for which it is applicable may be found in the Feller U.S. Pat. Nos. 4,399,696, 4,535,637, 4,829,833, 6,085,599 and 6,178,827.
Although it is believed that the foregoing recital of features and advantages may be of use to one who is skilled in the art and who wishes to learn how to practice the invention, it will be recognized that the foregoing recital is not intended to list all of the features and advantages. Moreover, it may be noted that various embodiments of the invention may provide various combinations of the hereinbefore recited features and advantages of the invention, and that less than all of the recited features and advantages may be provided by some embodiments.